Using piano wire as a motor hook; Using motor hooks with boattails

Using piano wire as a motor hook

Using motor hooks with boattails

Piano wire motor hook

Boattail motor hook

If you're like me, you prefer making your own motor hooks instead of buying them, but you find getting suitable material is a pain. Other than spent windshield wiper refills, the thin, springy material is indeed hard to come by. But piano wire is available at nearly every hobby shop, and it has the springy quality needed for motor hooks.

However, since it's round, it presents a new challenge when securing it to the motor tube. Since it's not flat, it wants to roll. But there's a solution.

Furthermore, many of today's motors are not all the same length, so you need flexibility in your motor mount for using different length motors.

To address the length issue, simply leave out the engine block from the motor tube, and apply a few wraps of 1/4" wide masking tape to the aft end of the motor. This "aft thrust ring" is sufficient up to H motors and maybe beyond.

But, since there's no "forward thrust ring" (ie, engine block), there's no way for a standard engine hook to poke through (at its forward end) since it might then interfere with the motor. And without that, the piano wire not only wants to roll, but to slide back and forth.

The mounting technique pictured above solves that and the rolling problem. An "S" curve is bent into the forward end of the hook, then that is curved to contour to the motor tube. A couple layers of gauze can be glued on to hold it in place. I used a nylon mesh material from the fabric store. It's kinda like wedding veil material.

Anyway, there are a variety of materials suitable for this. The only trick is if you're doing a minimum diameter bird and need to attach it to the airframe. In that case, you want it all to lay very flat so that there's not a lot of buildup when you apply filler over the glue.

I've used this piano wire hook setup on several rockets, and have had great results with it, and never a failure.

Many high performance rockets have boattails, and that often results in needing to friction fit the motors since it's difficult to have a motor hook or T-nuts (with Kaplow Klips) on a boattail. And friction fitting is a pain. So I came up with this solution.

Mount the motor hook as you normally would, or as shown at left, then attach your aft centering ring, slotted to accomodate the hook. Next, attach triangular balsa (or basswood or aircraft plyood) pieces on either side of the hook going from the aft centering ring and tapering to the motor tube.

The tailcone is slid in place with a small slit at its aft end to slide over the hook. Once the glue has dried, the slit can be expanded to open up the slot where the hook resides. The slot only needs to be opened as far forward as necessary to let the hook be bent out of the way while sliding the motor in. The slot need not be opened all the way to the centering ring; it's up to the modeler.

Here's one I did on a bashed Quest Big Betty.

Here are a couple pics of a motor hook in the MidgetT30's booster. They're almost in focus. I'd take some more, but the tube has been installed in the rocket :)

On the left, the S-curve is clearly seen. And the nylon mesh should be just visible.

On the right, the user will see how the hook was bent to contour to the motor tube.

4-23-2004